Good match up. Spinks defneisve style makes him incredibly hard to pin down. He looks so hittable, but just isn't. He's likely able to beat Johnson to the punch, but is he able to stop Johnson landing. If Johnson forces the pace, he should beat Spinks. If Johnson is content throwing at a low out put, he'll lose.
Ironically, I'd say the same thing about Johnson. He walked around casually with his hands low, but when you actually look at his fights, he was rarely hit.
It's the same with a lot of guys who break the rules at the top level. What they did, clearly worked for them, even if it isn't something 90% of boxers can pull off.